An early brake drum is disclosed in U.S. Pat. No. 2,087,062 which shows a drum brake assembly in which the brake shoes are operated by fluid pressure actuated pistons. The brake shoes are connected to the pistons in such a manner as to permit a swiveling action against the brake drum. Also known are ring disc brakes such as that of U.S. Pat. No. 3,170,542, wherein a ring disc rotated with the vehicle wheel and a caliper was mounted to a nonrotating torque member. The caliper held friction linings in position on both sides of the rotating ring disc and was hydraulically actuatable to apply such friction linings against the surface of the rotating ring disc. Another brake arrangement is shown in U.S. Pat. No. 3,245,499, wherein axially spaced, radially extending annular friction surfaces were nonrotatably mounted on a fixed frame member in concentric relationship with respect to the wheel axle. Annular friction discs were rotatably mounted to the wheel axle between the aforesaid nonrotating annular friction surfaces. Expandable actuating discs were disposed between the friction discs. The actuating discs were spread by a cam action to apply the friction discs against the friction surfaces, thereby providing vehicle braking. A similar disc brake assembly is shown in U.S. Pat. No. 3,342,290, wherein opposed radially extending disc surfaces rotate with the vehicle wheel rim. Brake shoes are mounted within the space between the disc surfaces. Upon application of the brake, hydraulic pressure drives a wedge between the brake shoes causing the brake shoes to spread apart into contact with the disc surfaces.
Drum brake assemblies in current use typically comprise one or more brake shoes carrying friction linings mounted on a nonrotating backing plate which extends radially from the wheel axis. The brake shoes are adapted for reciprocal motion to contact and retract from a rotating drum surface. The brake shoes are operated by a wheel cylinder actuated by hydraulic or pneumatic pressure. Thus, upon actuation of the wheel cylinder the brake shoes and linings are forced against the drum, whereby braking forces are transmitted to the vehicle wheel. The drum surface is the inner surface of an annular flange extending axially from a radially extending wall or plate mounted to the vehicle axle. Since the circumference of the drum surface is dictated generally by the size of the vehicle wheel, in the past to provide more effective braking and to avoid the buildup of excessive heat upon braking, it has been known only to increase the drum surface by increasing its axial dimension. Consequently, however, to provide structural stability to avoid radial distortion of the drum surface upon application of pressure against it by the brake linings, known vehicle brake drums necessarily have been of relatively massive, heavy construction. That is, upon actuation of the brake, the brake drum must be sufficiently rigid to overcome distortion due to pressure by the friction linings against the drum surface, notwithstanding that the axial dimension of the drum surface acts effectively as a large moment arm. In addition, known brake drum assemblies are relatively complex, comprising numerous components including the brake shoe/lining assembly, wheel cylinders, adjusting levers, cables and cable guides, various biasing springs, and automatic brake shoe position adjusting means.
It is an object of the present invention to provide a drum brake assembly which is less complex in design and assembly than known drum brake assemblies.
Another object of the present invention is to provide an improved and simplified drum brake suitable for motor vehicles and having good heat dissipation properties.
A particular object of the invention is to provide a drum brake assembly of equal or better efficacy than conventional drum brake assemblies and yet providing a weight saving over such conventional drum brake assemblies. Additional aspects and advantages of the invention will be apparent from the drawings and following description thereof.